1. Field of the Invention
The present invention relates to a damper and more particularly to a damper for suspension of an engine on a vehicle structure.
2. Description of the Prior Art
There is illustrated in FIGS. 1 and 2 a conventional damper of an engine mount which comprises a plurality of armatures 1, 2, one of which being connected to an engine and the other being connected to a vehicle structure such as a frame. A tubular elastic block of elastomer 3 is interposed between and fixedly attached to these armatures 1, 2, and within a bore defined by the armatures 1, 2 and the block 3, two chambers A, B are formed which are filled with a working fluid and communicate with each other through a hole 4 serving as an orifice. A partition plate 5 between said chambers A, B has its periphery rimmed with a rubber 7 and disposed movably within in a space between a shoulder 6a formed on the base plate 1 and a stop 6. The second chamber B defined above the partition plate 5 has its upper end sealably closed by a diaphragm 8 which is fixed by a pressure plate 9 on the armature 1.
The armature 2 is attached by a fixed bolt to the vehicle structure and the armature 1 is attached to the engine together with the pressure plate 9.
The damper dampens a vibration of the engine by converting the engine vibration into a change in volume of the first chamber A within the block 3 and suppressing a resulting change in pressure occurring within the chamber A by allowing restricted flow communication with the chamber B through the hole 4 of the partition plate 5. During this operation the partition plate 5 moves upwardly and downwardly between the shoulder 6a and the stop 6 in response to the pressure difference between both of the chambers A, B. In the case of small vibrations which result in the change in volume of the chamber A which can be followed by this upward and downward movements, the hole 4 formed through said partition plate 5 does not perform the dampening function. During this operation, the dampening of vibration is performed by the elastic deformation of the elastic block 3, only.
For proper operation of the damper illustrated in FIG. 1, the partition plate 5 itself must be of a sufficient thickness to withstand a pressure difference between the both chambers A and B and an orifice tube 10 should be attached to the partition plate 5 in such a manner as indicated by an imaginary line to enhance the orifice effect if the orifice effect by the hole 4 is found to be unsatisfactory, resulting in an increase in the inertia of the partition plate 5. This causes a problem in that the increased inertia prevents the partition plate 5 from moving in response to a pressure difference between the both chambers A and B which occurs in response to small vibrations of the engine. Another problem is that the workability in assembly of the partition plate is poor because it is to be assembled with the rubber 7 and stop 6.
Referring to FIG. 2, a second conventional damper is explained. This damper comprises two armatures 1a, 1b, and another two armatures 2a, 2b arranged above and below said armatures 1a, 1b, respectively. Elastic blocks 3a, 3b of elastomer are interposed respectively between the base plates 1a, 2a and between the base plates 1b, 2b. Two chambers A, B are formed within the elastic blocks 3a, 3b, filled with a working fluid and communicating with each other through a hole 4 serving as an orifice. A partition plate 5 defines chamber A, B. The armatures 2a, 2b are fixedly clamped to each other by an elongate bolt 11, which elongate bolt 11 extends through the hole 4 of the partition plate 5, so that the effective area of the hole 4 serving as the orifice is defined by a ring rubber 12 mounted on the partition plate 5 and the elongate bolt 11. The outer periphery of the partition plate 5 is movably disposed within a space between said armatures 1a, 1b, the space having a distance h. This damper operates in substantially the same manner as that of FIG. 1.
The damper shown in FIG. 2 suffers from the same problem as that shown in FIG. 1. The problem is in that the inertia of the partition plate 5 is so large that it can not respond well to small vibrations of an engine because of the necessity of sufficient thickness of the partition plate 5 for withstanding a great pressure difference between the both chambers A, B and because of the provision of the ring rubber 12. Another problem derived from the complicated configuration of the armatures 1a, 1b, 2a, 2b is that a great degree of accuracy in assembly is required to provide the desired dimension h and sufficient sealing effectiveness between the elastic blocks 3a, 3b and the partition plate 5.